1. Field of the Invention
The present invention relates to a nose seal assembly for establishing a seal between the assembly and the nose of an open ended hollow shaft upon relative rotational movement therebetween.
2. Description of the Prior Art
In the use of centrifugal chemical analysis apparatus, it is necessary to provide a fluid coupling means between stationary parts and rotating parts. In this respect, one centrifugal chemical analysis apparatus utilizes a transfer disc having a plurality of channels arranged in a spoke like configuration therein. Each channel includes at least three wells or chambers, one for receiving reagent, one for receiving sample, and an outer well or chamber in which the sample and reagent are mixed during rotation of the transfer disc.
Coaxial with the transfer disc is an annular member containing a plurality of reaction chambers or cuvettes. Each reaction chamber has an inner opening aligned with an outer opening in the wall of a mixing chamber in the transfer disc so that when the transfer disc and annular member are rotated, mixed sample and reagent flow by centrifugal force into the reaction chamber.
Also, each time the reaction chamber passes a fixed position in the centrifugal chemical analysis apparatus, light is passed through the reaction chamber to monitor the absorbance of the mixture.
A hollow shaft which is closed at its lower end and which is open at its upper end is mounted coaxial with the transfer disc in the centrifuge of the apparatus and a cover is provided for covering the transfer disc and the annular member. The hollow shaft has a plurality of radial ports therethrough communicating with the interior of the hollow shaft near the bottom closed end thereof. Each of these ports is aligned with a port in the transfer disc communicating with the inner chamber in a line of chambers. The upper open end of the shaft is referred to as the nose of the shaft and is coupled through a stationary nose seal assembly to tubings carrying compressed air, wash water or suction.
During the operation of the centrifugal chemical analysis apparatus, after a reaction is completed, compressed air is blown through the nose seal assembly and the rotating hollow shaft through the ports and into the chamber in the transfer disc to force liquid therein into the reaction chamber where the liquid is siphoned out of the apparatus. Then wash water is injected through the seal assembly and rotating shaft into the chambers followed by application of suction to create a bubbling or scrubbing action on the wash water which is being urged outwardly by centrifugal force and inwardly by suction. Then compressed air is again blown through the seal assembly and the hollow shaft into the chambers to assist the centrifugal action in pushing the wash water out to the reaction chambers where it is siphoned out of the apparatus.
In presently available chemical analysis apparatus of this type, such as the apparatus sold under the trademark ROTOCHEM by American Instrument Company, a division of Baxter Travenol Laboratories, Inc., of Silver Spring, Maryland, a nose seal assembly is provided which provides effective sealing. This nose seal assembly includes a wear pad or washer made of graphite filled phenolic material which is cemented to a heat dissipation disc of the nose seal assembly. The other side of the heat dissipation disc is cemented to a rubber washer which is cemented to a bushing which is coupled to a manifold to which the air, wash water and suction conduits are also coupled. The assembly is utilized with a nose on the shaft which is flat except for rounded inner and outer circular corners. In use, this nose seal assembly is very noisy causing squeaking and scraping sounds and after a certain amount of wear of the wear pad, the whole seal assembly must be replaced.
As will be described in greater detail hereinafter, the nose seal assembly of the present invention provides a more effective seal between the assembly and the nose of the shaft by providing an assembly with a releasably clamped wear pad which can be replaced without replacing the whole assembly, which utilizes a nose configuration which provides good sealing, low wear, and low noise, and which includes a resilient elastomeric mounting member for the wear pad which provides good compensation or "give" for a non-coplanar mating between the plane of the top of the nose and the plane of the wear surface of the wear pad.